Recently, in order to actualize the magnetic refrigerator in the high temperature region from 4K to room temperature, several investigators in Japan and USA have studied the problem of the magnetic refrigerants, the refrigeration cycles and the new type of magnetic refrigerators. In this review successive to the previous one by Ohtsuka the current works of those are introduced. This paper consists of the following four parts: 1) First, in order to make clear the direction of the investigation for the magnetic refrigerator, operations and physical charactor of the magnetic refrigerator by Brown are discussed precisely and it is pointed out that investigations on the magnetic refrigerant, heat exchange between the regenerator and refrigerant, and the thermal analysis of the fundamental magnetic refrigeration cycle are important. 2) Next, current investigations on two types of magnetic refrigerants, which have the large applied magnetic field dependence of the magnetic entropy change caused by its considerable increase of internal field near Tc and the rotation of the large magnetic anisotropic substance in the magnetic field, are cited and the origin of these phenomena is explained physically. 3) Then, we describe the investigations of heat exchange between the magnetic substance and heat transfer gas and of the thermal analysis of the refrigeration cycle. 4) Last, for examples of new types of magnetic refrigerators, rotational-cooling magnetic refrigerator by Barclay and regenerative magnetic expander (RME) by Barclay and Steyert are introduced.
Acousto-thermal and thermo-acoustic effects in tubes are discussed in terms of fluid mechanics. A fluid in a tube is assumed to be an ideal gas and basic equations of fluid mechanics are linearized. Averaging over the tube cross-section makes the problem into one-dimensional one. At first the discussion proceeds without viscosity and it becomes clear that thermal conductivity of gas play an important role. After that viscosity is included and effects of finite viscosity are discussed. Results obtained explain some qualitative features of experiments. Limitation of this linearized theory is also discussed.
The non-gray effect on the radiative heat transfer is studied. A well known formula using the total emissivity is not always fitted to an experimental fact, especially at cryogenic temperatures. We propose a formula for radiant energy flow per unit area emitted from a high temperature (T2) surface and absorbed at a low temperature one, Q=σT24×0.01100∑i=1E(λi) where σ Stefan-Boltzmann coefficient, and E the effective emissivity calculated from the emissivity on the high temperature surface and the absorptivity on the low temperature one at wavelength λi obtained from the selected ordinate method. Infrared spectral reflectances of a copper-oxide, an aluminum oxide on aluminum alloy, and an indium oxide coated glass are measured for estimation of the radiative heat transfer.
Fluid flow measurement technique by heating method, in which the flow quantity is calculated from heating quantity and the temperature difference between the outlet and inlet of the heating section, is described. This method is expected to be especially useful for the cryogenic fluid flow measurement, since it is generally low in velocity and therefore, the usual orifice method may not be applicable and also since very accurate temperature measurement up to the order of 0.01K is possible by the use of germanium thermometer in the cryogenic temperature region. This heating method was applied to cryogenic helium gas flow measurement and some technical know-how and the accuracy obtained are described.